A desirable characteristic for certain molecular sieve catalysts, regardless of the process of use, is that the finished or formulated catalyst be attrition resistant. Attrition resistance can refer to hardness as well as ability to absorb shock, since the catalyst will typically have to endure severe stress in commercial scale processes.
For example, WO 99/21651 describes a method for making molecular sieve catalyst that is considered relatively hard. The method includes the steps of mixing together a molecular sieve and an alumina sol, the alumina sol being made in solution and maintained at a pH of 2 to 10. The mixture is then spray dried and calcined. The calcined product is reported to be relatively hard.
U.S. Pat. No. 6,153,552 describes another method for making molecular sieve catalyst. The catalyst is made by mixing together a silicon-containing oxide sol as a binder material and a molecular sieve material. The pH of the mixture is adjusted prior to spray drying. Following spray drying, the catalyst material is calcined to form a finished catalyst product, which is reported to be relatively hard.
U.S. Pat. No. 6,455,628 describes a process for preparing an aqueous dispersion by wet milling an aqueous carrier medium, a particulate solid, and a polymeric dispersant that is composed of at least 50 wt % of a block copolymer.
U.S. Pat. No. 6,872,680 describes methods for making molecular sieve catalyst compositions having improved attrition resistance by forming a slurry by combining a molecular sieve, a binder, and a matrix material, wherein the slurry has a pH above or below the isoelectric point (IEP) of the molecular sieve.
U.S. Patent Application Publication No. 2007/0100187 describes processes for making attrition resistant molecular sieve catalyst compositions by initially mixing together catalyst components to form a slurry at a relatively low viscosity and high solids content using a rotor-stator mixer.
Attrition resistance continues to be a desirable characteristic in molecular sieve catalysts. As new process systems are developed, the ability of the catalyst to endure the stress of the process system is particularly important so as to increase the effective life of the catalyst in the reaction process. If the catalyst is not properly attrition resistant, it is likely to break apart at an early stage, meaning that the catalyst could only be effectively used for a relatively short period of time. Therefore, obtaining molecular sieve catalysts that have a high degree of attrition resistance are still sought. Methods that are particularly effective at making highly attrition resistant molecular sieve catalysts at commercial scale are in particularly high demand.
In addition, reducing or minimizing the energy used in mixing can be particularly advantageous, and may even be necessary, in methods for fabricating molecular sieve catalysts that have a high degree of attrition resistance.